Injection of a liquid such as a drug into a human patient, an agriculture animal, or pet is performed in a number of ways. One of the easiest methods for drug delivery is through the skin, which is the outermost protective layer of the body. It is composed of the epidermis, including the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale, and the dermis, containing, among other things, the capillary layer. The stratum corneum is a tough, scaly layer made of dead cell tissue. It extends around 10-20 microns from the skin surface and has no blood supply. Because of the density of this layer of cells, moving compounds across the skin, either into or out of the body, can be very difficult.
The current technology for delivering local pharmaceuticals through the skin includes transdermal patches, ionotophoresis, sonophoresis, and methods that use needles or other skin piercing devices. Invasive procedures, such as use of needles or lances, effectively overcome the barrier function of the stratum corneum. However, these methods suffer from several major disadvantages: local skin damage, bleeding, risk of infection at the injection site, creation of contaminated needles or lances that must be disposed of, and compliance issues associated with fear of needles. Further, when these devices are used to inject drugs in agriculture animals, the needles can break off and remain embedded in the animal. Needle free injection technologies provide an effective alternative route for drug delivery devoid of many of the issues associated with delivery by more conventional methods. However, many of the currently commercially available technologies use actuators, for examples springs or compressed gases, that allow little to no control over the pressure exerted on the drug during delivery.